A TALK ABOUT METEORITES. 371 



due to the fact that there are two distinct classes of meteorites, 

 irons and stones, the characteristics of which make it difficult to 

 assign a like origin to both. It is probable, however, that they 

 all belong to our solar system ; that they are revolving round the 

 sun in some different plane from the ecliptic, and that the earth 

 is constantly meeting them in its yearly journey. When they 

 come- into contact with our atmosphere, although they are moving 

 with planetary velocity — sometimes at the rate of forty-five miles 

 a second, more than twice as fast as the earth moves in its orbit — 

 their motion is rapidly reduced, owing to the resistance of the air, 

 so that in most cases they come to the ground like a spent cannon- 

 ball. Their passage through the air is only of a few seconds' 

 duration, yet the rapid reduction of velocity determines a great 

 heating effect, so that the meteorite, a moment before intensely 

 cold, is immediately fused on the surface, forming a coating vary- 

 ing from a fiftieth to a hundredth of an inch in thickness, and 

 this crust is one of the first characteristics by which a meteorite 

 is recognized. Moreover, the material burns away unevenly, form- 

 ing pittings or thumb-marks, resembling the marks left by the 

 fingers on a mass of putty — a character also observed on large 

 grains of partially burned powder picked up after the discharge 

 of large guns. The meteorite from Cynthiana, Ky., in the Har- 

 vard collection, shows similar marks though more in furrows, 

 made by a flow of the melted surface from the front to the back 

 of the mass during its passage. 



The unequal heating of meteorites by the atmosphere causes 

 pieces to crack off, and sometimes the whole mass explodes. In 

 addition, the air rushing in to fill the space behind the rapidly 

 moving body, causes a sound variously compared to claps of 

 thunder, firing of musketry, the tearing of calico, and the like — a 

 noise frequently heard after the passage of the meteorite, owing 

 to the circumstance that the sound travels so much more slowly 

 than the mass itself. Furthermore, the high temperature of the 

 surface causes the mass to glow with a brilliant light, making it 

 appear like a ball of fire, and visible at distances depending on its 

 height above the horizon, sometimes over an area of one thousand 

 miles. Thus a meteorite was seen in 1876 to pass over the States 

 of Kansas, Nebraska, Iowa, Missouri, Wisconsin, Illinois, Michi- 

 gan, Kentucky, Indiana, Ohio, West Virginia, and Pennsylvania ; 

 and explosions were heard like cannonading even to the distance 

 of one hundred and fifty miles from its course. Over Illinois it 

 was seen to break in pieces like a rocket, and over Indiana and 

 Ohio the pieces were computed to cover an area forty miles long 

 and five miles broad. At Rochester, Fulton County, Indiana, dur- 

 ing the meteorite's passage, a farmer heard the thud of something 

 striking the ground near his house, and in the morning found a 



